This invention relates to improvements in adjustable lumbar supports for seating and relates particularly but not exclusively to such adjustable lumbar supports for motor vehicles.
The lumbar support is provided by a waistband extending from one side of a seat frame to the other and the variation in support is achieved by altering the length of the waistband supported by two fixed points or by altering the distance between the ends of a fixed length waistband by suitable adjustment means from either or both ends of the waistband. In either case the radius of the arc of the waistband is altered to provide the adjustment or variation of the lumbar support provided for the occupier of the seat.
Examples of known adjustable lumbar support mechanisms incorporating a flexible waistband of inextensible material are described in British Patent 2035792 (Holdsworth); Australian Patent Application No. 80449/82 (Moriya et al), U.S. Pat. No. 4,462,635 (Lance) and international application publication No. WO 92/17096 (corresponding U.S. patent application Ser. No. 08/122,519, filed Sep. 17, 1993). These patents show differing mechanisms for providing adjustable lumbar support by means of a waistband. The Holdsworth and Moriya lumbar supports provide variable lumbar support by altering the distance between the ends of a fixed length waistband whereas Lance provides adjustment by varying the length of the waistband between two fixed anchorage or support points. In each case the variation of the distance between the ends of the fixed length waistband or the variation of the length of the waistband is accomplished by adjustment at or from one end only of the waistband.
As is known, the waistband extends across the seat behind the normal cushioning and other upholstery of the seat. It is customary at the present time to form the cushioning in the form of specially moulded foam plastic material seat squabs in one piece with the lumbar support waistband positioned behind the cushioning material when considered from the position of the occupier of the seat.
It is also customary, to obtain the desired degree of lumbar support, for the adjustment mechanism to be varied whilst the occupier of the seat is seated in the usual position.
It is also known that the length or curvature of the waistband of the Holdsworth, Moriya or Lance adjustable lumbar supports referred to above is biased to the position set by the adjustment means by the weight component of the occupier of the seat which is in the direction of the waistband. This weight component causes contact between the waistband and the cushioning material of the seat.
It has now been found that the nature of the materials of the waistband and the seat cushioning material is such that the friction between them gives the sensation of uneven lumbar support adjustment when the adjustment of the waistband occurs from one end only as is shown by Holdsworth, Moriya and Lance.
Such adjustable lumbar supports give the sensation of providing lumbar support adjustment in a greater degree towards that end of the waistband where the adjustment is being made to either the distance between the ends of a fixed length waistband or to the length of a waistband between two fixed points.
It is believed that the sensation or perception of uneven lumbar support adjustment is due to friction between the cushioning material of the seat and the waistband and the greater relative movement between the cushioning material and the waistband towards that end of the waistband at which adjustment occurs.
It is an object of the present invention to overcome the perceived disadvantages of the prior art adjustable lumbar support devices.